The present invention generally relates to amorphous silicon x-ray detectors. In particular, the present invention relates to the detection of electromagnetic radiation by an amorphous silicon x-ray detector for metal detection in x-ray imaging.
Digital imaging systems may be used to capture images to assist a physician in making an accurate diagnosis. Digital radiography imaging systems typically include a source and a detector. Energy, such as x-rays, produced by the source travel through an object to be imaged and are detected by the detector. An associated image processing system obtains image data from the detector and prepares a corresponding diagnostic image on a display.
The detector may be an amorphous silicon flat panel detector, for example. Amorphous silicon is a type of silicon that is not crystalline in structure. Image pixels are formed from amorphous silicon photodiodes connected to switches on the flat panel. A scintillator is placed in front of the flat panel detector. For example, the scintillator receives x-rays from an x-ray source and emits light of an intensity related to the amount of x-rays absorbed. The light activates the photodiodes in the amorphous silicon flat panel detector. Readout electronics obtain pixel data from the photodiodes through data lines (columns) and scan lines (rows). Images may be formed from the pixel data. Images may be displayed in real time. Flat panel detectors may offer more detailed images than an image intensifier and camera combination. Flat panel detectors may allow faster image acquisition than an image intensifier and camera combination depending upon image resolution.
Medical practitioners, such as doctors, surgeons, and other medical professionals, often rely upon technology when performing a medical procedure, such as image-guided surgery (“IGS”) or examination. An IGS system may provide positioning and/or orientation (“P&O”) information for the medical instrument with respect to the patient or a reference coordinate system, for example. A medical practitioner may refer to the IGS system to ascertain the P&O of the medical instrument when the instrument is not within the practitioner's line of sight with regard to the patient's anatomy, or with respect to non-visual information relative to the patient. An IGS system may also aid in pre-surgical planning.
The IGS or surgical navigation system allows the medical practitioner to visualize the patient's anatomy and track the P&O of the instrument. The medical practitioner may use the tracking system to determine when the instrument is positioned in a desired location or oriented in a particular direction. The medical practitioner may locate and operate on, or provide therapy to, a desired or injured area while avoiding other structures. Increased precision in locating medical instruments within a patient may provide for a less invasive medical procedure by facilitating improved control over smaller, flexible instruments having less impact on the patient. Improved control and precision with smaller, more refined instruments may also reduce risks associated with more invasive procedures such as open surgery.
Tracking systems used in surgical navigation systems may be optical, ultrasonic, inertial, or electromagnetic, for example. Electromagnetic tracking systems may employ coils as receivers and transmitters. An electromagnetic tracking system may be configured in an industry-standard coil architecture (“ISCA”), for example, although other configurations for electromagnetic tracking systems may also be used. The ISCA is characterized by three colocated orthogonal quasi-dipole transmitter coils and three colocated quasi-dipole receiver coils. Other systems may use three large, non-dipole, non-colocated transmitter coils with three colocated quasi-dipole receiver coils. Another tracking system architecture uses an array of six or more transmitter coils spread out in space and one or more quasi-dipole receiver coils. Alternatively, a single quasi-dipole transmitter coil may be used with an array of six or more receivers spread out in space.
The ISCA tracker architecture uses a three-axis quasi-dipole coil transmitter and a three-axis quasi-dipole coil receiver. Each three-axis transmitter or receiver is built so that the three coils exhibit the same effective area, are oriented orthogonal to one another, and are centered at the same point. The exact sizes, shapes, and relative-to-one-another positions of the transmitter and receiver coil-trios are measured in manufacturing. If the coils are small enough compared to a distance between the transmitter and receiver, then the coil may exhibit dipole behavior. Magnetic fields generated by the trio of transmitter coils may be detected by the trio of receiver coils. Nine transmitter-receiver mutual inductance measurements may be obtained. From these nine parameter measurements and the information determined in manufacturing, a position and orientation determination of the receiver coil-trio may be made with respect to the transmitter coil-trio for all six degrees of freedom.
In medical and surgical imaging, such as intraoperative or perioperative imaging, images are formed of a region of a patient's body. The images are used to aid in an ongoing procedure with a surgical tool or instrument applied to the patient and tracked in relation to a reference coordinate system formed from the images. Image-guided surgery is of a special utility in surgical procedures such as brain surgery and arthroscopic procedures on the knee, wrist, shoulder or spine, as well as certain types of angiography, cardiac procedures, interventional radiology and biopsies in which x-ray images may be taken to display, correct the P&O of, or otherwise navigate a tool or instrument involved in the procedure.
Several areas of surgery involve very precise planning and control for placement of an elongated probe or other device in tissue or bone that is internal or difficult to view directly. In particular, for brain surgery, stereotactic frames that define an entry point, probe angle and probe depth are used to access a site in the brain, generally in conjunction with previously compiled three-dimensional diagnostic images, such as MRI, PET or CT scan images, which provide accurate tissue images. For placement of pedicle screws in the spine, where visual and fluoroscopic imaging cannot capture an axial view to center a profile of an insertion path in bone, navigation systems have also been useful.
However, metal or other materials capable of distorting electromagnetic fields in the object being imaged can result in artifacts or distortions in the image. For example, metal in the area of the patient being x-rayed, such as pedicle screws in the spine, can cause streak artifacts. These distortions or artifacts may generally reduce the value of the image to the medical practitioner.
In the case of a three-dimensional (3D) image, these distortions or artifacts may have an even more pronounced effect. 3D volumetric imaging provides new diagnostic and clinical analysis tools to physicians. 3D images are created by acquiring a series of two-dimensional (2D) images at predetermined positions along an arc about a patient. Software applications using complex mathematical processes extract volume elements or “voxels” from the 2D images by using the image content (e.g., a black-and-white x-ray image) and positional information (e.g., where the image was positioned along an arc). The voxels may then be assembled into a three-dimensional image and then viewed from any angle. Artifacts or distortions in the 2D images from, for example, metal in the object being imaged, may be amplified through the use of the 2D images to create the 3D images. This amplification occurs in part because there is less data available in the 2D images, due to the artifacts and distortions, to properly assemble the voxels for the 3D image. Metal artifact reduction algorithms may be used to reduce the effects of the distortions or artifacts caused by metal in the object being imaged. Thus, it is highly desirable to determine when metal is present in the object being imaged so that techniques such as metal artifact reduction algorithms may be utilized.
Another potential source of artifacts or distortions in images are electromagnetic fields. An electromagnetic field affecting the detector may originate in part from an electromagnetic transmitter such as, for example, an electromagnetic transmitter in a surgical navigation system. One or more parts of the detector of the imaging system may be susceptible to electromagnetic fields. For example, the photodiodes, readout electronics, and/or wiring within an amorphous silicon flat panel x-ray detector may be affected by an electromagnetic field. These components may, for example, act as an antenna. The electromagnetic field may result in distortions or artifacts in the images read from the detector in part because the electromagnetic fields introduce spurious signals or noise into one or more of the components of the detector. This noise may appear as artifacts or distortions in the images read from the detector. Thus, it is desirable to detect electromagnetic fields so that distortions and artifacts caused by such fields may be compensated for.
Therefore, there is a need for compensating for electromagnetic fields affecting amorphous silicon x-ray detectors. Further, there is a need for detecting metal in x-ray imaging by electromagnetic radiation using an amorphous silicon x-ray detector.